EXPLORING THE PROKARYOTIC COMMUNITY ASSOCIATED WITH THE RUMEN CILIATE PROTOZOA POPULATION

Ciliate protozoa are an integral part of the rumen microbiome and were found to exert a large effect on the rumen ecosystem itself as well as their host animal physiology. Part of these effects have been attributed to their ability to harbor a diverse ecto- and endo-symbiotic community of prokaryotic cells. Little is known about the composition and function of the bacterial components associated with rumen protozoa and the extent of this association, despite their perceived importance and the wide variety of functions shown to occur in other environments.

In this study, we characterize the prokaryotic community associated with different protozoa population and compared their structure to the free-living prokaryotic population residing in the cow rumen. We observed that the structure and composition of the protozoa associated prokaryotic community differs significantly compared to the free-living community in terms of richness and composition. The methanogens proportion was significantly higher in all protozoa fractions compared to the free-living fraction, reaching up to 15% of the total prokaryotic community within the larger protozoa compared to 1.3% in the free-living fraction. The most prevalent family in the protozoa associated bacterial communities reaching up to 70% compared to 3% in the free-living fraction while the Prevotellaceae was the dominant family in the free-living community. Several taxa not detected or detected in extremely low abundance in the free-living community could be seen enriched in the protozoa associated bacterial community. These included members of the Endomicrobia class, a taxon previously identified as a protozoa symbiont in the termite gut. Together, our results show that rumen protozoa harbor a prokaryotic community that is compositionally different from its surrounding community, which may be the result of specific tropism between the prokaryotic community and protozoa towards either specific functional association or selective predation.